Alaska Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
623 PM EDT Sat Jun 26 2021
Valid 12Z Wed Jun 30 2021 - 12Z Sun Jul 4 2021
...Unsettled weather expected from portions of the Aleutians to
the Southern Coast...
...Overview and Guidance/Predictability Evaluation...
The latest models and ensembles continue to advertise a large
upper low that will drift slowly eastward along and just south of
the Aleutians for the end of the week. There is some indication
that this could split into two separate lows within an elongated
trough, with eastward progress being halted by an upper level
ridge axis over eastern mainland Alaska and western Canada.
Perturbations rounding the base of the trough will support a
couple of surface lows and accompanying cold fronts across the
Aleutians and the Gulf region. Troughing may also briefly move
through northern parts of Alaska early in the period before the
ridge axis builds in. At the surface, a quasi-stationary front is
expected to be present across northern portions of the Interior.
The deterministic guidance along with the ensemble means have a
very good overall depiction of the synoptic scale pattern across
the Alaska domain through Thursday. By Friday, the GFS becomes
more progressive with the upper low over the Alaska Peninsula,
whilst the best agreement supports the main low being over the
southern Bering Sea. By the end of the forecast period next
weekend, the ECMWF is to the west of the model consensus with the
upper trough/low over the Bering Sea.
...Weather/Threats Highlights...
The surface lows and fronts affecting the Aleutians towards the
middle to end of the week are expected to produce periods of
showers and gusty winds from the eastern Aleutians into the Alaska
Peninsula and Kodiak Island region. Some moderate to locally
heavy rainfall is likely for parts of this region, although exact
amounts remain uncertain. Gusty winds and rough surf may also
accompany these systems as they cross the region. To the north, a
cold front dropping through Northern Alaska may bring some modest
precipitation to parts of the North Slope region and Brooks Range.
As upper level ridging builds over the state by the end of the
week, temperatures should be near to above average, with highs
generally in the 70s for the lower elevations of eastern Alaska.
Southern Alaska and back to the Aleutians should remain near or
below normal temperature wise underneath mostly cloudy skies.
Hamrick
Additional 3-7 Day Hazard Information can be found on the WPC
medium range hazards chart at:
https://www.wpc.ncep.noaa.gov/threats/threats.php
WPC medium range Alaskan products including 500mb, surface
fronts/pressures progs and sensible weather grids can also be
found at:
https://www.wpc.ncep.noaa.gov/alaska/ak_5dayfcst500_wbg.gif
https://www.wpc.ncep.noaa.gov/alaska/akmedr.shtml
https://www.wpc.ncep.noaa.gov/alaska/ak_5km_gridsbody.html